1. Field of the Invention
The presently disclosed embodiments of the claimed invention relate to an image forming apparatus of a printer, a copy machine, or the like, and in particular, they relate to an image forming apparatus having plural image forming units.
2. Discussion of the Related Art
It is often desirable to form a high quality color image at a high speed by an image forming apparatus of a printer, a copy machine, a facsimile, or the like. Full-color tandem copy machines are known. Such tandem machines arrange four image forming units, yellow(Y), magenta(M), cyan(C), black(K), for example, in series, forming each toner image sequentially. Each of the toner images formed by the image forming units are overprinted (first transfer) to an intermediate transfer belt, which serves as an intermediate transfer body, before being transferred again (second transfer), all at one time, from the intermediate transfer belt to transfer paper. Subsequently, by fixing the toner image formed on the transfer paper, full-color as well as monochrome images may be produced.
In a conventional image forming apparatus that uses an intermediate transfer body, a photosensitive drum, which functions as an image carrier, is provided in each image forming unit. The photosensitive drum contacts the intermediate transfer belt laid across it, which is maintained in a tensioned condition by plural rollers. In conventional designs, when maintenance is necessary, for example replacing the photosensitive drum or other components, the photosensitive drums, which are in contact with the intermediate transfer belt, are pulled out individually.
In conventional systems, a guide rail is provided that allows the transfer belt to disengage from the photosensitive drum. This is described in pages 4 and 5 and FIG. 4 of Japanese Patent Laid-Open Publication No. 275987/2000. The guide rail system makes it possible to locate the transfer belt in precise relation to the photosensitive drum, while allowing the belt to be disengaged and the photosensitive drum to be pulled out for removal.